A few things to try to up the interest in eating is try topping the food with small amounts of:
catnip
parmesan cheese
BBQ chicken without the skin
deli meat
crushed kibble
melted butter
yogurt
any human food she likes
Did you try to put a dab of food on her paw? Is she licking it off? Might be enough to get her interested in food again
Right now the focus is to get her to eat anything, at this point it doesn't have to be cat food
You can also try to give her plain no spices added chicken human baby food, try cooked chicken breast, scrambled eggs, cooked ground beef, liver you can buy it from grocery store (if she'll eat raw meat you can try it uncooked or lightly sear the outside or fully cooked), cooked ham even the deli meat is usually a big hit
Call your vet as soon as they open to ask about using a different appetite stimulant since that one isn't working.
Did your vet mention giving Subcutaneous fluids for the kidney issue? I've dealt with kidney failure in cats and they always feel better after getting fluids - less tired, more apt to eat etc
